Regeneration maturity is determined using the mean diameter measure

Regeneration maturity is determined primarily by the growing stock’s mean diameter. Stem size development is the result of temperature sum, site type, tree species, number of thinnings and type of thinning. A stand is considered to be economically mature once its annual relative yield falls permanently below the target level set by the forest owner.
 
Except in the case of Northern Finland’s birch increment models, increment models are based on the principle that the majority of the growing stock in a stand that has reached regeneration maturity is composed of sawtimber. If a stand fails to reach the minimum limit set for regeneration maturity, e.g. due to its treatment history, such a stand can be regenerated on the basis of its age alone. When setting the limits for regeneration maturity, the current value of the net revenues to be obtained from selling the growing stock and a real interest rate of 2–3%have been employed.
 
Examples of regeneration maturity employing mean stand diameter (measured at 1.3 m above ground level)
 

Stand’s main tree species and site type	Southern Finland over 1,200 d.d	Middle Finland 1,000–1,200 d.d.	Northern Finland 750–1,000 d.d.
Scots pine on dryish upland site	25–30 cm	23–27 cm	22–26 cm
Norway spruce on moist upland site	26–30 cm	25–28 cm	22–25 cm
Silver birch on moist upland site	27–30 cm	26–28 cm	21–23 cm

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